This study was conducted at the open field in, Abnob, Assiut Governorate - Upper Egypt under field conditions during the two cotton seasons of 2017and 2018.The results indicated that the population of the cotton leafworm Spodoptera littoralis (Boisd.) moths in cotton plant by observing and recording moths in sex pheromone traps every three days. Spodopteralittoralishad seven peaks starting from the 1^stweek of May until the 3^rdweek of October during the two studied seasons. The highest number of average moths was recorded insex pheromone traps during the end of July which being 66.0 and 63.0moth /trap/ 3 night in both seasons, respectively. It was noted the predicted peaks of generations could be detected when the accumulated thermal units recorded 525.42 DD's.As recorded the peaks for the detected seven generations varied from -3 to +3 days from the observed peaks. For better prediction of the S. littoralis the period between the observed and expected peaks should be positive at least one or two days when early preparation of control materials are of great important, consequently, it is necessary to design an program for controlling this pest renewed annually depends on climate changes an addition to the use of insecticide program for better prediction and controlling of the cotton leafworm Spodoptera littoralis.